Harmonic Mitigation

In simple terms, harmonics are extra frequencies that when present in an electrical circuit, distort the AC sine wave. A harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency.

For example, if the fundamental frequency is f, the harmonics have frequencies 2f, 3f, 4f, . . . etc. Harmonic frequencies are equally spaced by the width of the fundamentalfrequency and can be found by repeatedly adding that frequency. In the case of the Australian electricity supply, the fundamental frequency is 50Hz. The frequencies of the harmonics are 100Hz, 150Hz, 200Hz, 250Hz, 300Hz, 350Hz and so on. 150Hz is called the 'third' harmonic (3 x 50Hz), 250Hz is called the 'fifth' harmonic (5 x 50Hz), etc. The presence of harmonics in an electrical system distorts the clean shape of a sine wave.

> Harmonic Mitigation Products

How do you know if you have harmonics in your electrical system?

If you occasionally experience some unexplained occurrences such as flickering lights, alarms going off, or MCB's, MCCB's, RCD's and Earth Leakage devices tripping for no apparent reason, you are most likely experiencing harmonics in your electrical environment. Other signs are cables running hot, hot switchboards or overheating motors. If you are replacing your motor's bearings & insulation often, that's a strong indication of the presence of harmonics.

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What are the effects of harmonics in your electrical system?

Harmonics are very harmful within an electrical system and can have serious consequences. For example, the presence of harmonics reduces the life of equipment. It is possible that the investment that you made in your motors & drives will not be realised if they are damaged and need replacing before their expected life span. This can be very expensive.

Harmonics cause things to run hot, which cause stress on the cables and equipment. In the long term, this degrades an electrical system. The presence of harmonics will also mean that although you will get billed for the power that you are supplied, a large percentage of that power may be unusable. Harmonic mitigation is taking action to minimise the presence of harmonics in your electrical system and can achieve great cost savings.

Variable Speed Drives (also known as Variable Frequency Drives) are prolific creators of harmonics in electrical systems and as a result, most of the harmonic mitigation effort focuses on the input side and output side of a VSD.

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Different types of Harmonic Mitigation devices?

Depending on the specific situation, there are a variety of products that are used to mitigate harmonics. Fuseco's Power Quality Consultants can assist by conducting a site analysis or simply providing advice based on the details of the particular electrical system. Here is a brief summary of the product groups:

Input (Line) side of the VSD (VFD)

1. Line Reactors

• Also known as Inductors, Chokes & Line Filters.
• For use on the input of a VSD / Inverter or other non-linear devices.
• Virtually eliminate nuisance tripping.
• Extend life of semiconductors.
• Reduce harmonic distortion.
• Reduce surge currents.
• Improve true power factor.

> Reactors

2. Passive Harmonic Filters

• Also known as 'Low Pass Filters'.
• For reducing harmonics at the VSD / Inverter or other non-linear devices.
• Reduction of harmonics to 5-6%
• Reduce cable heating and line losses.
• Improve power factor and reduce system loss.
• Minimise interference with other equipment.
• Improved system voltage/current waveform.
• Prevent nuisance tripping of fuse and circuit breakers.
• Meets the IEEE519 Standard.

> Passive Filters 

3. Active Harmonic Filters

• Mainly used for group harmonic compensation at the main switchboard.
• Reduction of harmonics to 5% or less.
• Reactive current control.
• Load side transient suppression.
• Load side surge suppression. Reduction of supply sags and surges.
• Improves electrical system efficiency.
• Reduces operations and maintenance costs.
• Meets the IEEE519 Standard.

> Active Filters 

Output (Load) side of the VSD (VFD)

1. Load Reactors

• Also known as Motor Chokes, Load Filters & Inductors.
• For use on the output of a VSD / Inverter or other non-linear devices.
• Protect motors from long lead effects.
• Reduce reflective currents.
• Reduce Harmonic Distortion.
• Reduce Surge Currents.
• Reduce Motor Temperature.
• Reduce Motor Audible Noise.

> Reactors 

2. dV/dT FLTERS

• dV/dT filters are designed to protect AC motors from the destructive effects of long lead peak voltages.
• Increase bearing life and up-time.
• Reduce common mode noise and currents.
• Prevent voltage spikes from exceeding 1kV.
• Reduction in motor peak voltages.
• Protection of motor insulation.
• Reduction of motor temperature.

3. Sine Wave Filters

• In addition to protecting the motor, the sine-wave filter also provides protection for the VSD/inverter.
• Unshielded motor cables can be used, lower project costs.
• Motor operating life is increased.
• Longer motor cables possible.
• Significantly lower eddy current and stray flux losses.
• Significant reduction of bearing currents.
• Eliminate torque ripple.
• Eliminate voltage wave reflection.
• Reduces motor noise, vibration and heat.
  

Site Analysis

Power quality audits can be carried out on your site by Fuseco's expert Power Quality team to assess your Harmonic Mitigation needs. A report will be presented to you outlining the results and any recommendations on solutions that may be needed for your electrical system to comply with acceptable harmonic levels outlined in IEEE 519.

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Solutions

Depending on the specific situation, there are a variety of products that are used to mitigate harmonics or reduce the effects of RFI. Fuseco's PQ Consultants are more than happy to assist in providing advice on your particular needs.

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> Power Quality Products

How can I find out more?

Schaffner have released an information booklet called "Basics in EMC & Power Quality".

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